1. Field of the Invention
This invention relates to a method and apparatus for reducing to acceptable limits the amount of toxic fumes, other vapors, and particulate matter in the air within a manufacturing plant for polyvinyl chloride materials, or other materials presenting similar pollution problems.
2. Description of the Prior Art
In the manufacture of polyvinyl chloride film or sheet materials, a thermal plastic resin, a plasticizer, a stabilizer, fillers and pigments are combined and mixed together in a blender. The composition is then further mixed and heated within mixing rolls. The composition is then conveyed while still hot to a calendaring machine to be rolled into a film or sheet. The heating causes some of the materials in the composition to evaporate, and in other ways causes smoke, oily vapor or fumes, dust and odors to be produced. Herein the term "vapor" is used to describe the entire fluid by-products of the manufacturing process and the term "particulate matter" is used to describe the small solid by-products of such process and dust drawn in from the region about the equipment.
It is known to use exhaust ducts and suction fans located over the heating and mixing equipment for collecting and removing the undesirable vapors and particulate matter. However, the known exhaust ducts and suction systems have not been particularly effective. They do not remove enough of the undesirable substances. It does not help to increase the exhaust and suction capacity of the fans because if this were to be done it would also be necessary to increase the temperature of the composition during mixing, and such a change would have an adverse effect on the quality of the product to be manufactured. Also, if the dust in the room is stirred up unnecessarily, such as by increasing the suction, and this dust adheres to the composition, it may show up as foreign matter on the film or sheet product, or cause damage such as the opening up of pin holes in the surface of such product.
The fault of the conventional exhaust systems could be avoided by locating each piece of machinery used in the manufacturing process within a separate room and then regulating the air and ventillation for each room so that both an adequate temperature is maintained and the proper amount of ventilation is provided for each part of the operation. However, the cost of providing separate rooms for each piece of equipment would be prohibitive. Furthermore, the separate room arrangement would not provide adequate protection against undesirable vapors for all stages of operation. Current government standards prohibit even a small amount of certain toxic gases within a work area. It would not be possible to locate the equipment which emits such toxic gases in a separate ventilated room and by this procedure reduce the amount of the toxic gas in the room down to below the permissible level.